Mountain and fog models have been added

[serkanMzlm]

🎉 New feature

Summary

• Fog has been added to the mountainous environment
• The collision part is closed by default.
• This application is created using DEM(Digital Elevation Model).
• The collision part can be created with simpler shapes.

Test it

# The first step is to download the GitHub repository
git clone git@github.com:serkanMzlm/gz-sim.git

# The second step is to add the 'examples' directory of the repository to GZ_SIM_RESOURCE_PATH
export GZ_SIM_RESOURCE_PATH=/home/${USER}/gz-sim/examples
cd gz-sim/examples/worlds/

# The third step is to run the file
gz sim -r mountain_fog.sdf 

[azeey]

Yes, I would suggest uploading to Fuel unless we have a specific reason to add it to the source code. Do you mind doing that @serkanMzlm?

[serkanMzlm]

@azeey The main reason might actually be to demonstrate DEM usage

[azeey]

@azeey The main reason might actually be to demonstrate DEM usage

We already have dem_moon.sdf and dem_volcano.sdf, so I don't think we need more examples.